I would not use free space optics for this but there are licensed wireless backhauls that can do this with high enough capacity and reliability. Feel free to contact me directly (contact info in the about me section of this site) for more info.
FSO was one of neatest things I learned to solve the "fiber is expensive to run in cities" problem back when I studied wireless. Just one class on that. I'd like to know why you recommend against FSO for this, if there's any time you would recommend it for smaller players, or drawbacks compared to LTE. I just haven't seen anyone bring up FSO in a while and wondered why.
Possibly you know more about it than I do! When I've used it (admittedly only once) it was very susceptible to anything in the air (dust, rain, snow) and was not very reliable over even a very short distance (less than 30meters iirc). I guess I can see how it could work with lots of buffering so there's not much packet loss but it seems like that would negatively affect latency.
Well, they told us they work around a mile or so in good conditions with more in near-perfect conditions. They could miss a lot of packets if weather interference happened. So, they were often paired up with another link (slow wired or fast wireless) as backup for highest-priority stuff. They were also sold as more secure from taps. They were also really expensive back when I studied them. Aside from being low volume, that was probably because (as our course materials said) they were deployed in areas where laying fiber was really, really expensive. So, maximizing profit meant charging significantly less than that but not too much less, ya know? ;)
A long time ago, I looked it up again to see what the cheapest, budget setup was. I still have this bookmark of an open design I found:
